The invention relates generally to highly accurate measurements and more particularly to a fault tolerant system and method for accurately determining a revolution rate of a rotating gear.
Known measurement systems can measure the revolution rate of a rotating gear based on the elapsed time for a point on the gear to pass over a sensor during a complete rotation. Such a rotating gear can be, for example, a turbine or compressor.
Such measurement systems, however, present special challenges when used for applications involving high reliability. For example, transient noise if not properly rejected can cause measurement errors. Such transient noise can be introduced into the measurement system by, for example, low amplitude or slow input signals; electromagnetic compatibility (EMC) transients; or module hot inserts or spare removals. Similarly, power surges if not properly addressed can cause the measurement system to fail. In addition, any sensor failure (e.g., relating to a broken sensor or broken wire to the sensor) should be detected quickly so that repairs can be made and the proper performance of the measurement system is assured.
Thus, a need exists for a fault tolerant system and method for accurately determining a revolution rate of a rotating gear.
An apparatus comprises an edge detector, a memory and a pulse-input engine. The edge detector is configured to receive an input signal and a counter signal. The edge detector is further configured to send a set of time values based on the input signal and the counter signal. Each time value from the set of time values is uniquely associated with a detected edge transition from the input signal. The memory is coupled to the edge detector. The memory is configured to receive from the edge detector the set of time values. The memory is configured to store the set of time values. The pulse-input engine is coupled to the memory. The pulse-input engine is configured to measure a set of pulse-to-pulse delays based on the set of time values stored in the memory.